Effect of mA Reduction on Image Quality Parameters and Patient Dose in Computed Tomography Imaging

Abstract

Purpose: To establish the extent of dose reduction that can be achieved using a computed tomography (CT) quality assurance phantom with various user-defined protocols at different milliamperage (mA) settings and kilovoltage peak (kVp) without affecting image quality.

Methods: Images of a CT quality assurance phantom containing line-pair patterns and 3 tissue-equivalent inserts in water were acquired with different mA settings on 4 different CT scanners. The kVp was kept constant at 120 while the mA was changed in increments of 20, from 30 mA to 190 mA. Three images from each series acquired at different mA settings were selected: one each for the quantitative analysis of spatial resolution, contrast-to-noise ratio (CNR), and image noise using image analysis freeware.

Results: Statistical analysis was carried out with a statistical probability of P < .05 indicating significant difference. Results of the statistical analysis revealed significant differences in the CNR of all 3 types of tissue-equivalent inserts (P < .001) and in image noise (P < .001) as the mA was changed. However, changes in mA did not produce significant differences in the spatial resolution of the images (P > .06).

Conclusion: A radiation dose reduction of 25% was achieved in 4 different CT scanners without significantly affecting the 3 image quality parameters.